Size- and Shape-Controlled Synthesis and Properties of Magnetic–Plasmonic Core–Shell Nanoparticles

Abstract

Magnetic-plasmonic core-shell nanomaterials offer a wide range of applications across science, engineering and biomedical disciplines. However, the ability to synthesize and understand magnetic-plasmonic core-shell nanoparticles with tunable sizes and shapes remains very limited. This work reports experimental and computational studies on the synthesis and properties of iron oxide-gold core-shell nanoparticles of three different shapes (sphere, popcorn and star) with controllable sizes (70 to 250 nm). The nanoparticles were synthesized via a seed-mediated growth method in which newly formed gold atoms were added onto gold-seeded iron oxide octahedrons to form gold shell. The evolution of the shell into different shapes was found to occur after the coalescence of gold seeds, which was achieved by controlling the amount of additive (silver nitrate) and reducing agent (ascorbic acid) in the growth solution. First principles calculation, together with experimental results, elucidated the intimate roles of thermodynamic and kinetic parameters in the shape-controlled synthesis. Both discrete dipole approximation calculation and experimental results showed that the nanopopcorns and nanostars exhibited red-shifted plasmon resonance compared with the nanospheres, with the nanostars giving multispectral feature. This research has made a great step further in manipulating and understanding magnetic-plasmonic hybrid nanostructures and will make important impact in many different fields.

Synthesis and properties of magnetic-optical core–shell nanoparticles

“…36, 71, 72 In 2009, Goon et al developed an approach to directly make PEI-coated IO NPs and grew Au shells via repeated hydroxylamine reduction deposition on the PEI-coated IO NPs (Figure 2B). 71 IO NPs were prepared by precipitation of iron sulfate in a basic solution followed by oxidization with potassium nitrate at 90 °C in the presence of branched PEI (MW ~25,000) in an oxygen-free environment.…”

“…We recently developed a facile method for the synthesis of uniform IO-Au core-shell NSTs (Figure 4B) 72 with all steps performed in aqueous solutions. In our studies, octahedral Fe 3 O 4 NPs capped with PEI (edge length ~ 35 nm) were synthesized by precipitating ferrous sulfate in a base solution followed by oxidation with KNO 3 at 90 °C in the presence of branched PEI (MW ~ 25,000).…”

“…72 By following the growth process with TEM, it was found that the IO-Au core-shell nanospheres grew at a faster rate than the popcorns and stars. For spheres, the Au seeds coalesced within 5 min and formed continuous Au shells within 20 min.…”

“…However, in our recent studies, we found that increasing the Au shell thickness led to an increase of the magnetic properties of IO-Au core-shell nanopopcorns at 10K (Figure 6C). 72 The particles are capped with CTAB that binds to Au via Br − and is counterbalanced by CTA + in a bilayer structure. 98–100 Thus, charge transfer between Br − and Au may occur, which would enhance the electron mobility and, thus, the surface induced magnetism of Au.…”

Assumption-free morphological quantification of single anisotropic nanoparticles and aggregates

“…[12][13][14] In addition, the reactivity of NPs increases proportionally with the number of atoms on the surface. However, quantitative results for these vital morphological properties have not been fully addressed.…”